This invention relates to a process for treating used cooking oil or fat from frying operations such as industrial frying operations in order to remove impurities such as free fatty acids from the cooking oil or fat. More particularly, this invention relates to a system, preferably an automated system, for treating used cooking oil or fat that may be run continuously, thus providing for a more efficient process of treating used cooking oil.
Cooking oils and fats are employed in general for the cooking or frying of foods such as chicken, fish, potatoes, potato chips, vegetables, and pies. Such frying may take place in a restaurant wherein food is prepared for immediate consumption, or in an industrial frying operation where food is prepared in mass quantities for packaging, shipping, and future consumption.
In a typical restaurant frying operation, large quantities of edible cooking oils or fats are heated in vats to temperatures of from about 315xc2x0 F. to about 400xc2x0 F. or more, and the food is immersed in the oil or fat for cooking. During repeated use of the cooking oil or fat, the high cooking temperatures, in combination with water from the food being fried, cause the formation of free fatty acids (or FFA). An increase in the FFA decreases the oil""s smoke point and results in increasing smoke as the oil ages.
Industrial frying operations involve the frying of large amounts of food for delayed consumption. Often, this is a continuous operation with the food being carried through the hot oil via a conveyor.
Industrial fryers of meat and poultry must follow the guidelines of the FDA Food Safety and Inspection Service (FSIS) Meat and Poultry Inspection Manual. The following are excerpts from that manual:
Section 18.40 Frying (a) Meat
Length of time fats and oils may be used for deep fat frying varies with temperature, quality of new fat added daily, and fat treatment during use. Suitability of these fats for further use can be determined from degree of foaming during use or from color, odor, and flavor.
Fat or oil should be discarded when it foams over the vessel""s side during cooking, or when its color becomes almost black as viewed through a colorless glass container.
Section 18.40 Frying (b) Poultry (5) Fat Acceptability
Used fat may be made satisfactory by filtering, adding fresh fat, and cleaning the equipment regularly.
Large amounts of sediment and free fatty acid content in excess of 2 percent are usual indications that frying fats are unwholesome and require reconditioning or replacement.
Industrial fryers of meat and poultry, in general, use the 2% free fatty acid (FFA) limit, or less if mandated by their customers, as their main specification for oil quality.
In addition to hydrolysis, which forms free fatty acids, there occurs oxidative degeneration of fats which results from contact of air with hot oil, thereby producing oxidized fatty acids (or OFA). Heating transforms the oxidized fatty acids into secondary and tertiary by-products which may cause off-flavors and off-odors in the oil and fried food.
Caramelization also occurs during the use of oil over a period of time, resulting in a very dark color of the oil which, combined with other by-products, produces dark and unappealing fried foods.
Because of the cost resulting from the replacing of the cooking oils and fats after the use thereof, the food industries have searched for effective and economical ways to slow degradation of fats and oils in order to extend their usable life.
U.S. Pat. No. 4,112,129, issued to Duensing, et al., discloses a composition comprised of diatomite, synthetic calcium silicate hydrate, and synthetic magnesium silicate hydrate may be employed for reclaiming used fats and oil.
U.S. Pat. No. 4,681,768, issued to Mulflur, et al., discloses a process for treating used cooking oil or fat by contacting used cooking oil or fat with a high surface area amorphous synthetic magnesium silicate having a surface area of at least 300 square meters per gram.
U.S. Pat. No. 5,597,600, issued to Munson, et al., discloses the treatment of cooking oil or fat with magnesium silicate and at least one alkali material to reduce the content of free fatty acids in the oil or fat.
In present systems for treating used cooking oil or fat, however, the frying system is shut down periodically in order to remove the oil or fat from the fryer to a batch treatment tank where a purifying material is mixed for a specified time and then removed by filtration. The oil or fat then is ready to return to the fryer.
It is an object of the present invention to provide a filter system, which may be an automated system, for treating used cooking oil or fat wherein used cooking oil or fat may be treated continuously without shutting down the frying system.
In accordance with an aspect of the present invention, there is provided a process for treating used cooking oil or fat. The process comprises: (a)passing the used cooking oil or fat from a cooking oil or fat source to a holding vessel; (b)contacting the used cooking oil or fat with a predetermined amount of purifying material upon accumulation of a first predetermined amount of the oil or fat in the holding vessel; (c)passing the used cooking oil or fat and the purifying material from the holding vessel to a filter apparatus upon accumulation of a second predetermined amount of the oil or fat in the holding vessel, wherein the second predetermined amount of oil or fat is greater than the first predetermined amount of oil or fat, and whereby upon passing of the used cooking oil or fat and the purifying material from the holding vessel to the filter apparatus, the purifying material becomes entrained in the filter apparatus; and (d)passing the used cooking oil or fat from the filter apparatus to the source.
In one embodiment, step (a) comprises passing the used cooking oil or fat through a first transport line from said source to a first diverting valve. The used cooking oil or fat then is passed through a second transport line from said first diverting valve to a second diverting valve. The used cooking oil or fat then is passed through a third transport line from the second diverting valve to the filter apparatus, and the cooking oil or fat is passed through the filter apparatus and then through a fourth transport line from the filter apparatus to the holding vessel.
In another embodiment, in step (b), the used cooking oil or fat is contacted with the purifying material in the second transport line upon accumulation of the first predetermined amount of the cooking oil in the holding vessel. Upon contact of the used cooking oil or fat with the purifying material in the second transport line, the second diverting valve is diverted such that the used cooking oil or fat is passed from the source through the first transport line, the first diverting valve, the second transport line, the second diverting valve and through a fifth transport line from the second diverting valve to the holding vessel until the used cooking oil or fat is accumulated in the holding vessel at the second predetermined level.
In yet another embodiment, step (c) comprises diverting the first diverting valve such that the used cooking oil or fat and the purifying material are passed from the holding vessel to a sixth transport line from the holding vessel to the first diverting valve, and then are passed through the second transport line from the first diverting valve to the second diverting valve. The used cooking oil or fat and the purifying material then are passed through the third transport line to the filter apparatus. The used cooking oil or fat and the purifying material then are passed through the filter apparatus, whereby the purifying material becomes entrained in the filter apparatus. The used cooking oil or fat then is passed through the fourth transport line from the filter apparatus to the holding vessel.
In another embodiment, step (d) comprises diverting the first diverting valve such that the used cooking oil or fat is passed through the first transport line, the first diverting valve, the second transport line, the second diverting valve, and the third transport line to the filter apparatus. In general, the oil passes through the filter apparatus for a period of time of from about 10 minutes to about 20 minutes, preferably from about 15 minutes to about 20 minutes, more preferably about 20 minutes. The used cooking oil or fat then is passed through a seventh transport line from the filter apparatus to the source. The first diverting valve then is diverted such that the used cooking oil or fat contained in the holding vessel is passed from the holding vessel through the sixth transport line, the first diverting valve, the second transport line, the second diverting valve the third transport line, the filter apparatus, and the seventh transport line to the source or to a holding vessel which feeds the source.
In a preferred embodiment, residual oil or fat then is removed from the filter apparatus, and the residual oil or fat is passed from the filter apparatus to the holding vessel. The used purifying material then is removed from the filter apparatus.
In one embodiment, a gas is introduced into the filter apparatus, whereby the gas transports the residual oil from the filter apparatus to the holding vessel.
In another embodiment, a gas is introduced into the filter apparatus, whereby the gas removes the purifying material from the filter apparatus.
Examples of the gas, which may be employed in removing residual oil and/or the purifying material from the filter apparatus, include, but are not limited to, nitrogen and compressed air. In a preferred embodiment, the gas is nitrogen.
Purifying materials which may be employed include, but are not limited to, magnesium silicate; calcium silicate; activated carbon; silica gel; magnesium phosphate; and alkali materials such as alkaline earth metal hydroxides, alkaline earth metal oxides, alkaline metal carbonates, alkali metal bicarbonates, sodium sesquicarbonate, alkaline earth metal carbonates, and alkali metal silicates. The purifying material can include one or more of the above components.
In one embodiment, the purifying material comprises magnesium silicate.
In general, the magnesium silicate is a magnesium silicate which is acceptable as a filter aid in food processing applications. For example, the Food Chemical Codex, Third Edition, gives the following specifications for a synthetic magnesium silicate which is acceptable in food processing and industrial frying operations:
In one embodiment, the magnesium silicate is an amorphous synthetic magnesium silicate having a surface area of at least 300 square meters per gram, and preferably has a surface area from about 400 square meters per gram to about 700 square meters per gram, and more preferably has a surface area from about 400 square meters per gram to about 600 square meters per gram. In addition, such magnesium silicate is preferably employed as coarse particles, with at least 75%, and preferably at least 85% of the particles having a particle size which is greater than 400 mesh, and with no more than 15%, and preferably no more than 5%, all by weight, having a particle size greater than 40 mesh. In most cases, the average particle size of the magnesium silicate employed in accordance with the present invention is in the order of but not limited to 20-75 microns. It is to be understood, however, that the magnesium silicate may have a particle size different than the preferred size.
In addition, the hydrated magnesium silicate which is employed in accordance with a preferred embodiment of the present invention generally has a bulk density in the order of from 15-35 lbs./cu. ft., a pH of 7-10.8 (5% water suspension) and a mole ratio of MgO to SiO2of 1:1.8 to 1:4.
The following is a specification and typical value for a magnesium silicate which is employed in accordance with a preferred embodiment of the present invention:
A representative example of such a synthetic magnesium silicate having a surface area of at least 300 square meters per gram is available as Magnesol(copyright) Polysorb 30/40, a product of the Dallas Group of America, Inc., Whitehouse, N.J., and also is described in U.S. Pat. No. 4,681,768.
In another embodiment, the magnesium silicate is an amorphous, hydrous, precipitated synthetic magnesium silicate which has been treated to reduce the pH thereof to less than about 9.0. As used herein, the term xe2x80x9cprecipitatedxe2x80x9d means that the amorphous hydrated precipitated synthetic magnesium silicate is produced as a result of precipitation formed upon the contact of a magnesium salt and a source of silicate in an aqueous medium.
For purposes of the present invention, the pH of the magnesium silicate is the pH of the magnesium silicate as measured in a 5% slurry of the magnesium silicate in water. The pH of the treated magnesium silicate in a 5% slurry preferably is from about 8.2 to about 8.9, and more preferably from about 8.5 to about 8.8, and most preferably is about 8.5. Examples of such a treated amorphous hydrous precipitated synthetic magnesium silicate are available as Magnesol(copyright) XL and Magnesol(copyright) Dalsorb(copyright) F, products of the Dallas Group of America, Inc., Whitehouse, N.J., and also are described in U.S. Pat. No. 5,006,356.
In yet another embodiment, the magnesium silicate is a magnesium silicate which has a surface area of from about 50 square meters per gram to about 150 square meters per gram. Preferably, such a magnesium silicate has a mole ratio of MgO to SiO2 of from about 2:2.6 to about 1:3.4, and a pH (5% water suspension) of from about 9.5 to about 10.5. An example of such a magnesium silicate is available as Magnesol(copyright) HMR-LS, a product of the Dallas Group of America, Inc., Whitehouse, N.J.
In a further embodiment, the magnesium silicate has a pH (5% water suspension) of from about 9.0 to about 9.5.
In another embodiment, the magnesium silicate may be in the form of talc.
It is to be understood, however, that the scope of the present invention is not to be limited to any specific type of magnesium silicate or method for the production thereof
In one embodiment, in addition to magnesium silicate, the purifying material further comprises at least one alkali material selected from the group consisting of alkaline earth metal hydroxides, alkaline earth metal oxides, alkali metal carbonates, alkali metal bicarbonates, sodium sesquicarbonate, alkaline earth metal carbonates, and alkali metal silicates.
In one embodiment, the ratio of magnesium silicate to alkali material in the purifying material is generally at least 1.8:1, preferably at least 9:1, and generally does not exceed 32:1, and in most cases does not exceed 19:1, all by weight. Thus, in a preferred embodiment, based on the two components, the magnesium silicate is present in the purifying material in an amount of from about 65 wt. % to about 97 wt. %, preferably from about 90 wt. % to about 95 wt. %.
In one embodiment, the at least one alkali material is an alkaline earth metal hydroxide.
Preferably, the alkaline earth metal hydroxide is calcium hydroxide (Ca(OH)2).
In another embodiment the at least one alkali material is an alkaline earth metal oxide. Alkaline earth metal hydroxides which may be employed include, but are not limited to, magnesium oxide (MgO) and calcium oxide (CaO).
In another embodiment, the at least one alkali material is an alkali metal carbonate. Alkali metal carbonates which may be employed include, but are not limited to, sodium carbonate (Na2CO3).
In another embodiment, the at least one alkali material is an alkali metal bicarbonate. Alkali metal bicarbonates which may be employed include, but are not limited to, sodium bicarbonate (NaHCO3), and potassium bicarbonate (KHCO3).
In yet another embodiment, the at least one alkali material is sodium sesquicarbonate (Na2CO3.NaHCO3.2H2O).
In another embodiment, the at least one alkali material is an alkaline earth metal carbonate. Alkaline earth metal carbonates which may be employed include, but are not limited to, calcium carbonate (CaCO3).
In another embodiment, the at least one alkali material is an alkali metal silicate.
Alkali metal silicates which may be employed include, but are not limited to, sodium metasilicate (Na2SiO3).
In another embodiment, the at least one alkali material is present in the purifying material in an amount of from about 3 wt. % to about 35 wt. %, preferably from about 5 wt. % to about 20 wt. %, with the remainder being magnesium silicate, based on the two components.
The process of the present invention is applicable particularly to industrial flying operations. In one embodiment, at least 1 wt. % of the purifying material is added, based on the weight of the used cooking oil or fat, to the used cooking oil or fat, preferably at least 1.5 wt. % of the purifying material is added, based on the weight of the used cooking oil or fat. In general, the amount of purifying material employed does not exceed 2 wt. %, based on the weight of the used cooking oil or fat.
In another embodiment, the purifying material comprises calcium silicate.
In yet another embodiment, the purifying material comprises activated carbon.
In still another embodiment, the purifying material comprises silica gel.
In a further embodiment, the purifying material comprises magnesium phosphate.
It is to be understood, however, that the scope of the present invention is not to be limited to any specific purifying materials.
The selection of an optimum amount of purifying material is dependent upon a variety of factors, including, but not limited to, the frequency of the treatments and the condition of the oil and the products fried. The purifying material is employed in an amount effective to reduce free fatty acid or color or other contaminant levels so as to extend the period of use of the oil. The maximum amount will be determined by required oil quality, economics, and filtration flow properties in the operation.